1. Field of the Invention
The present invention relates to an ink-jet recording method and an ink-jet ink, and particularly to an ink-jet recording method and an ink-jet ink, by which ejection responsiveness and ink droplet properties can be improved, and an ink tank and a cartridge equipped with a head, both containing this ink-jet ink.
2. Description of the Related Art
In ink-jet recording, various investigations have heretofore been made for the purpose of achieving good ejection of an ink. In particular, regarding methods for preventing defective ejection caused by bubbles remaining within a nozzle of a head or mixed therein, proposals have been made from many points of view, such as nozzle design and ink design. For example, Japanese Patent Application Laid-Open No. 2002-80768 discloses a method that an antifoaming agent such as siloxane is contained in ink compositions for a piezo-ejection system.
When such additives are contained in an ink mainly composed of water, additives having high stability at temperatures before and under an operating environment are selected. The additives include surfactants. Various functions of such a surfactant are utilized for ink-jet inks. Representatively, a nonionic surfactant is used as a component of an ink for the purpose of ensuring desired penetrability of the ink into recording media such as paper. In this case, it is said that its cloud point is preferably at least 60° C. in such a manner that the surfactant can exhibit the desired function in an operating environment of an ink-jet recording apparatus (Japanese Patent Application Laid-Open No. 2001-354880).
On the other hand, an ink-jet head by a system that thermal energy is utilized to cause film boiling, thereby applying an ink within a flow path from an ejecting portion to a recording medium is also put to practical use, and a great number of inventions are proposed and carried out.
In the ink-jet system that thermal energy is utilized to cause film boiling, thereby applying an ink within a flow path from an ejecting portion to a recording medium, a process of generation, growth and disappearance of bubbles attending on film boiling on a surface at which heat from a heating element (heater) acts on the ink is repeated in the flow path for every application of an ejection signal. The ink is applied to the recording medium in the form of droplets from the ejecting portion by receiving a pressure attending on the generation of bubbles. In the case of this system, when a part of the bubbles generated by the heat from the heater remains within the flow path, bubbles are naturally generated at a temperature under an operating environment of the apparatus, or bubbles are mixed into the flow path from a liquid chamber or the like, pressure transmission to the ink upon the generation of the bubbles on the surface of the heater is affected, which may form the cause of the deterioration of ink ejection properties such as deterioration of responsiveness to ejection signals, deformation of ink-droplet form, defective ejection of ink droplets and deterioration of ink droplet impact accuracy in some cases. Incidentally, with respect to the natural generation of bubbles at the temperature of the operating environment of the apparatus, minute bubbles are generated due to lowering of solubility of dissolved gasses in the ink when the temperature of the ink within the flow path is raised by increase of the number of times of ejection per unit time, and in some cases, these bubbles may become great bubbles which affect the ejection properties by their growth or bonding. Accordingly, it is important from the viewpoint of preventing the natural generation of bubbles to cause the bubble process to functionally progress to prevent unnecessary temperature rise of the ink within the flow path.
Methods for preventing the bubbles from remaining in or being mixed into the liquid chamber and flow path include a method that the antifoaming agent mentioned above is contained in the ink. The antifoaming agent has at least one of a function of inhibiting generation of bubbles and a function of making it easy to extinguish bubbles already generated. Various substances are investigated as foam inhibitors or antifoaming agents for ink-jet inks. The bubbles within the flow path can be extinguished to some extent by containing the foam inhibitor or antifoaming agent in the ink, however, the solubility of substances investigated as the foam inhibitors or antifoaming agents may be low in many cases. When such a substance is contained in the ink in an amount of producing the antifoaming effect, the foam inhibitor or antifoaming agent separates from the ink and adheres to members in contact with the ink and the periphery of an ejecting portion of the ink, which may become a new cause of defective ink ejection in some cases. In particular, in the Bubble-Jet system that thermal energy is utilized, a drive system is damaged by the adhesion of the foam inhibitor or antifoaming agent to the surface of the heater, so that defective ink droplet ejection may be caused in some cases.
On the other hand, the cloud points of additives contained in an ink are selected from the viewpoint of ensuring the solubility of the additives in the ink in the operating environment of a recording apparatus and preset to a temperature not lower than the temperature of the opening environment of the recording apparatus. In other words, the cloud points of the additives are not positively utilized for improving the ink ejection properties, and moreover no proposal for the cloud point properties of liquid media containing the additives is put.